Netuptake of sulphate and its transport to the shoot in tobacco plants fumigated with H2S or SO2

Abstract

In tobacco plants the net uptake of sulphate and its transport to the shoot were determined after cultivation with low, normal, and high sulphate supply. The relative amount of the sulphate taken up that was transported to the shoot was used as a measure of xylem loading. Net uptake of sulphate and its transport to the shoot were low in tobacco plants grown with low sulphate, and high in plants cultivated with high sulphate. Xylem loading, however, was relatively low in tobacco plants grown with high sulphate and relatively high in tobacco plants grown with low sulphate supply. Pre-culture in low sulphate containing nutrient solution also resulted in a high proportion of the absorbed sulphate being transported into the xylem if normal sulphateconcentration was supplied afterwards. Fumigation with H2S or SO2 reduced net uptake of sulphate in tobacco plants grown with normal, but not with high sulphate supply. Sulphate transport to the shoots was diminished by H2S or SO2 fumigation in tobacco plants grown with normal and high sulphate supply. Also the relative amount of the sulphate taken up that was transported to the shoot was lowered by fumigation with H2S or SO2 in tobacco plants grown with normal sulphate supply. Apparently, the diminished sulphate transport to the shoot upon H2S or SO2 fumigation can only partially be explained by a smaller sulphate uptake. Sulphur nutrition of tobacco plants also seems to be controlled by xylem loading of sulphate. The possible role of glutathione as a signal regulating sulphur nutrition of tobacco plants upon fumigation with H2S and SO2 is discussed.